When sending an email to a recipient, it may happen that the receiving server doesn’t accept your email. The email can’t be delivered and bounces.
The receiving server reports back to our system that your email couldn’t be delivered. The causes for bounces can be versatile.
In general, each server can send completely individual bounce messages. There is no standard.
The following overview is a list of the most common bounce feedbacks that reach us:
|host is unknown / host not found|
|invalid adress / invalid recipient|
|mailbox not found / mailbox is unavailable|
|no mailbox here by that time|
|no such user|
|recipient e-mail adress unknown|
|user unknown / unknown user|
Filtering by Receiving Server
|mail was identified as spam|
|only registered users may use this system|
|recipient address rejected|
|relay not permitted|
Receiving Server Hardware Problems
|error writing message|
|message could not be stored|
|relay access denied|
|mailbox does not exist|
|mailbox has been deactivated / disabled / discontinued|
|mailbox is full|
|user has exhausted allowed storage space|
The notifications said: 550 and said: 553 are often used by servers to indicate a spam classification.
Please note: We recommend implementing the steps from this help center post to optimize the deliverability of your newsletter.
Help & Support
If you have any questions or need further assistance, please contact our service team at any time.